The invention relates to an aqueous polymer dispersion comprising from 0.1 to 10 parts by weight per 100 parts by weight of polymer of an emulsifier A) having a phosphate group, wherein said emulsifier consists at least 50% by weight of ethylene oxide and propylene oxide groups and the proportion of said ethylene oxide groups and propylene oxide groups is in each case at least 10% by weight, based on the overall amount of ethylene oxide and propylene oxide groups.
The invention also relates to the use of the aqueous polymer dispersions as binders in paints and anticorrosion coatings.
Aqueous polymer dispersions comprising an emulsifier having phosphate groups are known, for example, from DE-A-2743764, EP-A-421909 and EP-A-221498. DE-A-2743764 relates to polymer dispersions which are used in paints. The emulsifier is an alkanephosphoric acid or ester thereof. EP-A-421909 describes, inter alia, emulsifiers having phosphate groups and ethylene oxide groups. The polymer dispersions are used as binders for coating compositions. The anticorrosion coating materials of EP-A-221498 comprise a polymer with a copolymerized emulsifier. The emulsfier consists of a phosphate group, propylene oxide groups and an ethylenically unsaturated group.
EP-A-115468 discloses the use of a mixture of an emulsifier having phosphate groups and an emulsifier having ethylene oxide and propylene oxide groups.
The purpose of emulsifiers is to stabilize emulsifier monomer droplets and the polymer particles, obtained after polymerization, in the aqueous phase. The desired aim is of course to achieve a sufficient stabilization with the minimum quantity of emulsifier. Coagulation has to be avoided.
On subsequent use, the emulsifier remains in the coating composition and so also effects the properties of the resulting coating. In many cases, emulsifiers are responsible for the formation of bubbles and unevenness in the surface of the coating.
Where the composition is used as a binder for paints, the emulsifier is additionally desired to allow a high pigment concentration in the aqueous dispersion and to leave the pigment binding capacity of the polymer as high as possible. Low pigment binding capacity in the polymer leads to relatively poor mechanical stability in the coating and so, for example, to inadequate wet abrasion resistance.
In the case of anticorrosion coating materials an additional desire is for the emulsifier to contribute to the corrosion protection.
It is therefore an object of the present invention to provide emulsifiers which go as far as possible toward meeting the requirements regarding the stability of polymer dispersions and the surface quality of coatings produced from them. For paints utility, moreover, there is a desire for a high pigment binding capacity and, in the case of anticorrosion coating materials, for good corrosion protection.
We have found that this object is achieved by the aqueous polymer dispersions defined at the outset. We have also found that the aqueous polymer dispersions can be used as binders in paints and anticorrosion coatings.
The emulsifier present in the aqueous polymer dispersion is preferably a compound consisting at least 70% by weight of ethylene oxide and propylene oxide groups.
An essential feature of the emulsifier is that it comprises both ethylene oxide groups and propylene oxide groups.
The proportion of ethylene oxide groups is at least 10% by weight, preferably at least 40% by weight, based on the molar weight of the emulsifier.
The proportion of propylene oxide groups is at least 10% by weight, preferably at least 20% by weight, based on the molar weight of the emulsifier.
The molar weight of the emulsifier is preferably from 400 to 2000 and, with particular preference, from 600 to 1600 g/mol.
The emulsifier is preferably of the formula 
where 
R is C1-C18-alkyl
x, y, w, z are each an integer from 0 bis 30,
x+w is at least 1
y+Z is at least 1
n is 1 or 2
B is a mono- or divalent cation
a, c are each 1 or 2 with a*c=3-n
R is preferably C10-C16-alkyl. The sum x+w is preferably from 6 to 20 and, with particular preference, from 10 to 14. The sum y+z is preferably 2 to 10 and, with particular preference, from 3 to 7. Both w and z are preferably 0.
B is preferably a monovalent cation, especially of Na, K, NH3 or H; accordingly, c=1 and a=1 or 2.
Compounds of this kind are obtainable, for example, under the trade name Lutensit(copyright) (BASF).
The aqueous polymer dispersion of the invention comprises the emulsifier preferably in amounts of from 0.1 to 5 parts by weight and, with particular preference, from 0.2 to 3 parts by weight per 100 parts by weight of polymer.
The polymer consists preferably of
a) from 40 to 100% by weight, preferably from 60 to 100% by weight and, with particular preference, from 80 to 100% by weight of at least 1 principal monomer and
b) from 0 to 40% by weight, preferably from 0 to 25% by weight, with particular preference from 0 to 15% by weight of further copolymerizable monomers.
Principal monomers a) are selected from C1-C20-alkyl (meth)acrylates, vinyl esters of carboxylic acids of up to 20 carbons, vinylaromatic compounds of up to 20 carbons, ethylenically unsaturated nitriles, vinyl halides, vinyl ethers of alcohols of 1 to 10 carbons, aliphatic hydrocarbons of 2 to 8 carbons and 1 or 2 double bonds, or mixtures of these monomers.
Examples that may be mentioned are C1-C10-alkyl (meth)acrylates, such as methyl methacrylate, methyl acrylate, n-butyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate.
In particular, mixtures of the alkyl (meth)acrylates are also suitable.
Examples of vinyl esters of carboxylic acids with 1 to 2 carbons are vinyl laurate, stearate, propionate and acetate and also Versatic acid vinyl ester.
Suitable vinylaromatic compounds are vinyltoluene, xcex1- and p-methylstyrene, xcex1-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene and, preferably, styrene. Examples of nitriles are acrylonitrile and methacrylonitrile.
The vinyl halides are chloro-, fluoro- or bromo-substituted ethylenically unsaturated compounds, preferably vinyl chloride and vinylidene chloride.
Examples of vinyl ethers are vinyl methyl ether or vinyl isobutyl ether. Preference is given to vinyl ethers of alcohols of 1 to 4 carbons.
Hydrocarbons of 2 to 8 carbons and two olefinic double bonds that may be mentioned are butadiene, isoprene and chloroprene.
Suitable monomers (a) are preferably the alkyl (meth)acrylates, preferably C2-C10-alkyl acrylates and methacrylates, and the vinylaromatic compounds, and also mixtures of these compounds.
Very particular preference is given to methyl methacrylate, n-butyl acrylate, n-hexyl acrylate , octyl acrylate, 2-ethylhexyl acrylate and styrene, and also mixtures of these monomers, as monomers (a).
Further monomers b) are, for example, hydroxy-containing monomers, especially C1-C10-hydroxyalkyl (meth)acrylates, (meth)acrylamide, ethylenically unsaturated acids or acid anhydrides, especially carboxylic acids, such as (meth)acrylic acid or itaconic acid, or dicarboxylic acids, such as maleic acid or fumaric acid. Examples of further monomers b) also include crosslinking monomers, such as butanediol diacrylate or divinylbenzene.
The polymer can also be of multistage construction. In this case the stages differ in their monomer composition. The monomers of one stage are preferably polymerized to the extent of at least 80% by weight, with particular preference at least 90% by weight, based on the sum of the monomers of the respective stage, before beginning with the addition of the monomers of the next stage.
A multistage construction is not necessary in the context of the present invention. However, it has been observed that a multistage construction results in a lower minimum film-forming temperature with simultaneous good blocking resistance (virtually no sticking of coated substrates to one another on stacking).
Particular preference is given in this context to a two-stage construction.
The stages called I and II below contain preferably the following amount of monomers, based on the polymer:
I: from 5 to 80% by weight, with particular preference from 10 to 60% by weight
II: from 20 to 95% by weight, with particular preference from 90 to 40% by weight.
The monomer composition of the stages differs preferably in the glass transition temperature Tg, the Tg of the monomers of a stage being calculated by the method of FOX (FOX, Bull. Physics Soc. 1,3 (1956, p. 123)).
Preferably, the difference between the Tg of stage I and II is at least 5xc2x0 C., with particular preference at least 10xc2x0 C. However, the difference is generally no greater than 40xc2x0 C.
Preferably, the more hydrophilic stage has the lower Tg: irrespective of whether it has been polymerized first or second, the more hydrophilic stage in the finished polymer is located on the outside, i.e., as the shell. The more hydrophobic stage generally forms the core.
Preferably, stage I is the more hydrophilic stage; that is, it is formed from monomers which in their totality are more hydrophilic than the monomers of stage II.
The polymer dispersions can be prepared conventionally from the monomers by emulsion polymerization techniques which are general knowledge, using the customary emulsifiers, dispersants and initiators.
Suitable dispersants for carrying out free-radical aqueous emulsion polymerizations are conventionally employed emulsifiers or protective colloids in amounts of from 0.1 to 5% by weight, in particular from 0.2 to 3% by weight, based on the monomers. As dispersant it is preferred to use solely the emulsifier A) described at the outset or mixtures of emulsifiers consisting at least 50% by weight, in particular at least 75% by weight, of emulsifier A).
Other common emulsifiers are, for example, alkali metal salts of higher fatty alcohol sulfates, such as sodium n-lauryl sulfate, ethoxylated C8-C10-alkylphenols with a degree of ethoxylation of from 3 to 30, and ethoxylated C8-C25 fatty alcohols with a degree of ethoxylation of from 5 to 50. Further suitable emulsifiers are given in Houben-Weyl, Methoden der organischen Chemie, Volume XIV, Makromolekulare Stoffe [Macromolecular substances], Georg Thieme Verlag, Stuttgart, 1961, pages 192 to 209.
Suitable protective colloids are natural substances of high molecular mass, such as starch, methylcellulose, pectins and gelatin, and synthetic substances, such as polyvinyl alcohol and polyvinylpyrrolidone. Further protective colloids are described at length in Houben-Weyl, op. cit., pages 411 to 420.
Suitable polymerization initiators are all those capable of triggering a free-radical emulsion polymerization in aqueous media. They are generally employed in amounts of from 0.1 to 10% by weight, preferably from 0.2 to 4% by weight, based on the monomers. Customary compounds are inorganic peroxides, such as sodium and ammonium peroxodisulfates and hydrogen peroxide, organic peroxides, such as dibenzoyl peroxide or tert.-butyl hydroperoxide and azo compounds, such as azodiisobutyronitrile. These initiators are suitable for the customary reaction temperatures for free-radical emulsion polymerizations: from 50 to 100xc2x0 C. Where lower reaction temperatures are desired, of about 40 to 60xc2x0 C., redox systems, such as combinations of per compounds and a reductive coinitiator, are preferred over the sodium salt of the hydroxymethanesulfinic acid, ascorbic acid or iron(II) salts.
The preparation of aqueous polymer dispersions by the technique of free-radical emulsion polymerization is conventional. (cf. Houben-Weyl, op. cit., page 133 ff.).
It has been found particularly suitable to employ a feed technique, starting from an initial charge consisting of a portion of the monomers, generally up to 20% by weight, water, emulsifier and initiator. The remainder of the monomers and any regulators, in emulsified form, and, in addition, an aqueous solution of further polymerization initiators, are added in accordance with the progress of polymerization.
Where the emulsifier A), or the total amount of emulsifier A) desired, is not used as dispersant during the emulsion polymerization, the desired amount of emulsifier A) can also be added subsequently to the aqueous polymer dispersion obtained.
Preferably, the emulsifier A) is used as an emulsifier in the emulsion polymerization as described above. The use of other dispersants is unnecessary.
The aqueous polymer dispersion of the invention preferably has a solids content of from 35 to 65 and, with particular preference, from 45 to 55% by weight.
The glass transition temperature Tg of the copolymers is preferably within the range from xe2x88x9260 to 140xc2x0 C. and, with particular preference, within the range from 0 to 70xc2x0 C. (calculated in accordance with Fox, Bull. Physics Soc. 1, 3 (1956), p.123).
The polymer dispersion of the invention is notable for high stability with virtually no coagulation.
The polymer dispersion of the invention can be used as a binder for coating compositions, such as for lacquers, protective coatings, paper slips, decorative coatings, paints, adhesives, coatings on textiles, and as binders for unbonded fiber nonwovens.
Appropriate auxiliaries can be added for the various utilities, examples being flow control agents, thickeners, defoamers, fillers, pigments, dispersing auxiliaries for pigments etc. The coatings can be obtained by applying the coating compositions to appropriate substrates, such as metal, plastic, wood, paper and textiles, and by drying, if appropriate, at ambient or elevated temperature.
The coatings obtained feature a uniform surface and, in particular, freedom from bubbles.
The polymer dispersion of the invention is particularly suitable as a binder for anticorrosion coating materials and for paints.
In the case of anticorrosion coating materials, it is preferred to use polymer dispersions of the invention having a Tg of from 20 to 60xc2x0 C.
In addition to the polymer dispersion the anticorrosion materials may also include anticorrosion agents, such as corrosion inhibitors or active anticorrosion pigments, such as zinc phosphate.
Even without further anticorrosion agents, the polymer dispersion of the invention has a good corrosion protection effect.
In the case of paints, it is preferred to use polymer dispersions of the invention having a Tg of from xe2x88x9255 to 90xc2x0 C., with particular preference from xe2x88x9210 to 80xc2x0 C. and, with very particular preference, from 0 to 60xc2x0 C.
Paints, and especially emulsion paints, are one of the largest product groups of the paints and coatings industry (see Ullmanns Enzyklopxc3xa4die der technischen Chemie, 4th ed., Volume 15, Verlag Chemie, Weinheim 1978, p. 665). Emulsion paints generally include a film-forming polymer as binder and at least one inorganic pigment as colorant, as well as inorganic fillers and auxiliaries, such as defoamers, thickeners, wetting agents and, if appropriate, film-forming auxiliaries.
The quality of emulsion paints is critically determined by the ability of the film-forming polymer to carry out uniform binding of the nonfilm-forming constituents, the pigments and inorganic fillers. The pigment binding capacity of the binder plays a particularly important part in emulsion paints having a high content of inorganic pigments and fillers, characterized by a pigment volume concentration (p.v.c.) of  greater than 40%. The p.v.c. is usually defined as the quotient of the overall volume of the solid inorganic constituents (pigment+fillers) divided by the overall volume of the solid inorganic constituents (pigments and fillers) and of the polymer particles of the aqueous binder polymer dispersion; see Ullmanns Enzyklopxc3xa4die der technischen Chemie, 4th edition, Vol. 15, p. 668). A low pigment binding capacity leads to poor mechanical stability of the coating, which is manifested, for example, in low wet abrasion resistance. High wet abrasion resistance, however, is required in particular for washable emulsion paints. It is also necessary to ensure that the binder has a sufficiently low film-forming temperature to allow the coating composition to be processed even at low temperatures. At the same time, the binder polymer must not be too soft, so as to ensure sufficient strength, or too tacky, so as to prevent soiling.
A further important property of emulsion paints is the blocking resistance of the coatings, by which is meant minimal sticking of the coating film to itself under pressure and elevated temperature (good blocking resistance).
The paints (emulsion paints) of the invention comprise pigments and fillers, preferably in amounts such that the p.v.c. is from 15 to 85% and, with particular preference, from 25 to 55%.
Examples of typical pigments are titanium oxide, preferably in the rutile form, barium sulfate, zinc oxide, zinc sulfate, basic lead carbonate, antimony trioxide, and lithopones (zinc sulfide+barium sulfate). However, the emulsion paints may also comprise color pigments, such as iron oxides, carbon black, graphite, luminescent pigments, zinc yellow, zinc green, ultramarine, manganese black, antimony black, manganese violet, Paris blue or Schweinfurt green. In addition to the inorganic pigments, the emulsion paints of the invention may also include organic color pigments, examples being sepia, gamboge, Cassel brown, toluidene red, para red, Hansa yellow, indigo, azo dyes, anthraquinonoid and indigooid dyes, and also dioxazine, quinacridone, phthalocyanine, isoindolinone and metal complex pigments.
Suitable fillers include alumosilicates, such as feldspars, silicates, such as kaolin, talc, mica, magnesite, alkaline earth metal carbonates, such as calcium carbonate, in the form of calcite or chalk, for example, magnesium carbonate, dolomite, alkaline earth metal sulfates, such as calcium sulfate, silica, etc. The fillers can be employed as individual components although it has been found in practice that filler mixtures, such as calcium carbonate/kaolin or calcium carbonate/talc, are particularly suitable.
To increase the hiding power and to save on the use of white pigments it is common to employ finely divided extenders, such as finely divided calcium carbonate or mixtures of various calcium carbonates with different particle sizes. To adjust the hiding power, the shade and depth of color, it is preferred to employ blends of color pigments and extenders.
The emulsion paints of the invention are stable fluid systems which can be used to coat a host of substrates. Examples of suitable substrates are wood, concrete, metal, glass, ceramics, plastic, plasters, wall coverings, and coated, primed or weathered substrates.
The coatings produced using the emulsion paints of the invention are notable for high wet abrasion resistance and good adhesion in the wet state. Moroever, the coatings are not tacky, and feature high blocking resistance.